The file that’s hardest to get back after a wipe is never the one you remembered to back up. It’s the one you forgot existed — a browser bookmark folder, a decade of iMessage history, a license key pasted into a text file on the Desktop three laptops ago. Time Machine catches your Documents folder. It does not catch the seventeen places macOS quietly lets you store things that aren’t files at all.

I’ve reformatted enough Macs to stop trusting “just do a Time Machine backup” as a complete plan. It’s a good first step and a bad last one. What follows is the checklist I actually run before an erase-and-install, ordered by how often people forget each item — not by folder structure.

Why “Just Use Time Machine” Isn’t Enough

Time Machine backs up your file system — Documents, Desktop, Applications, most of your Library folder. It does a genuinely good job of that. What it doesn’t do is surface the things that live outside the file system’s mental model: state stored inside a browser’s own database, credentials in a password manager that syncs but wasn’t confirmed to have synced, a license activation tied to a hardware ID that a factory reset will silently burn.

The actual failure mode isn’t “Time Machine didn’t back up my files.” It’s “I restored from Time Machine and everything looked fine, until three weeks later I needed a two-factor recovery code that lived in an app I never thought to check.” Three weeks is exactly long enough that the old drive has already been wiped for parts, sold, or given away — which is why this has to be a checklist run before the erase, not a recovery plan for after.

Step 1: The Things That Aren’t Files

Start here, because these are the items a full disk image will still miss if you don’t handle them explicitly.

  • Password manager export. Whatever you use — a browser’s built-in vault, a dedicated app — export an encrypted backup file, not just a “sync status: OK” checkmark. Sync confirms the cloud copy exists; it doesn’t confirm you can get into the new machine before the old one is gone.
  • Two-factor authenticator seeds. If your authenticator app doesn’t support cloud sync or a documented export, you need the setup QR codes or manual seed keys for every account, written down somewhere that survives the wipe. Losing 2FA seeds is the single most common way people get permanently locked out of their own accounts after a reformat.
  • Software license keys. Grep your email for “license key,” “activation code,” and “serial number” before the wipe, while you can still search your own Mail.app archive locally. Keys tied to a hardware fingerprint (some pro audio and video tools do this) may need a manual deactivation on the old machine first, or you burn an activation slot for nothing.
  • SSH keys and GPG keys. ~/.ssh/ and your GPG keyring don’t back themselves up anywhere by default. Copy the whole .ssh folder and export your GPG private keys (gpg --export-secret-keys -a > private-keys-backup.asc) before you forget these exist, because a wiped Mac doesn’t ask nicely for the key back.
  • Browser data beyond bookmarks. Saved form-fill data, extension settings, and site-specific logins that were never synced to an account. If you’re changing browsers or accounts as part of the wipe, export bookmarks explicitly rather than trusting an account sign-in to pull everything.

Step 2: The Full System Backup

With the invisible state handled, the file system backup is the easy part — but do it in a way you can actually verify, not just start and walk away from.

# Confirm Time Machine actually completed, don't assume it
tmutil latestbackup
tmutil compare -a

tmutil latestbackup tells you the timestamp of the most recent completed backup — not “in progress,” completed. If that timestamp is from six weeks ago, you don’t have a backup, you have a false sense of one.

For anything you want reachable without restoring a whole Time Machine volume — the folders you’ll actually open in the first week on the new setup — a plain file copy to an external drive or cloud storage is worth doing alongside Time Machine, not instead of it:

rsync -avh --progress ~/Documents ~/Desktop ~/Pictures /Volumes/Backup/

rsync shows you a running file count and resumes cleanly if it’s interrupted, which cp -R on a multi-hundred-gigabyte Pictures folder will not forgive you for testing.

Step 3: Application-Specific Exports

Some data lives inside an app’s own format and needs an explicit export, or a Time Machine restore hands you a database file with nothing that can open it usefully:

  • Mail.app — if you’re not using IMAP (where the server is the source of truth), export mailboxes via Mailbox → Export Mailbox.
  • Notes.app — export as PDF or use File → Export as PDF per folder if you’re not staying inside iCloud sync.
  • Messages — iMessage history lives in a SQLite database at ~/Library/Messages/chat.db. iCloud Messages sync covers most people; if you’ve disabled it, copy that file directly before the wipe.
  • Photos library — if it’s not fully in iCloud Photos, the entire .photoslibrary package needs to move as one unit, not be picked apart file by file.

The pattern across all four: an app-specific format is a bet that the same app will be there to read it back. Where the option exists, export to a plain format (PDF, .mbox, a flat file) that doesn’t depend on it.

Step 4: Deauthorize Before You Erase

This step gets skipped because it doesn’t feel like “backing up” — it’s the opposite direction, removing this machine’s access rather than saving its data. Skip it and you find out the hard way, usually as a support ticket to someone else’s company:

  • Sign out of iMessage and FaceTime (Settings → your name → iMessage/FaceTime) — otherwise a new owner’s number can occasionally get tangled with old message routing.
  • Deauthorize Mac App Store / iTunes-family software if you’re not staying signed into the same Apple ID going forward.
  • Sign out of iCloud last, after everything above, so the sign-out itself doesn’t race a still-running sync and leave it half-uploaded.

Step 5: Verify Before You Erase — Not After

The checklist above is only as good as the verification step nobody wants to spend the extra fifteen minutes on. Before you touch Disk Utility:

  1. Mount the backup drive on a different Mac, or at minimum a different user account, and open three files at random from three different backed-up folders.
  2. Confirm the password manager export file actually opens and decrypts — an export that silently failed is worse than no export, because you’ll trust it.
  3. Check that tmutil latestbackup timestamp is from today, not from whenever you last remembered Time Machine existed.

Fifteen minutes of verification here is the difference between a wipe and a five-year data loss with extra steps. Erase Assistant doesn’t ask you to confirm any of this — it asks if you’re sure, and “sure” is not the same question as “verified.”